A LAN is a high-speed network that supports many computers connected over a limited distance (e.g., under a few hundred meters). A Virtual Local Area Network (VLAN) is mechanism by which a group of devices on one or more LANs is configured using management software so that they can communicate as if they were attached to the same LAN, when in fact they are located on a number of different LAN segments. After a VLAN has been created, individual switch ports (also referred to as “access ports”) are assigned to the VLAN. These access ports provide a connection for end-users or node devices, such as a router or server. A router is simply a device or, in some cases, software in a computer, that determines the next network point to which a packet should be forwarded toward its destination.
Bidirectional Forwarding Detection (BFD) is a network protocol, standardized in an Internet Engineering Task Force (IETF) working group, which is used to detect faults between two forwarding engines (e.g., routers or switches). In a typical application, BFD may require 50-150 ms to detect a link failure. According to BFD, sessions are explicitly configured between L3 endpoint neighbors—neighbors at Physical layer L1, Logical Layer L2 over switches or IP Datagram Layer over Routers. A session may operate either in asynchronous mode or demand mode. In asynchronous mode, both endpoints periodically send “Hello” packets to each other. (A Hello packet is basically a “keep alive” message sent by one device to another to check that the connectivity—over physical link, hardware and software paths—between the two L3 Neighbors is operating. The BFD hello mechanism provides detection of failures in a path between adjacent L3 Neighbors, linked over physical media, switches, and routers, switching and routing over forwarding engines, or on any kind of path between systems, including virtual circuits and tunnels.) If a number of the hello packets are not received in a timely fashion, a BFD session between L3 neighbors is considered down. In other words, failure of reachability to a neighbor, for whatever reasons, is detected when packets are not being received or sent. In demand mode, no Hello packets are exchanged after the BFD session is established; rather, it is assumed that the endpoints have another way to verify connectivity to each other, perhaps on the underlying physical layer. However, either host may still send Hello packets if deemed necessary. Regardless of which mode is in use, either endpoint may also initiate an “Echo” function. When this function is active, a stream of Echo packets is sent, and the other endpoint then sends these back—loopbacks—to the sender via its forwarding plane. This function is used to test the forwarding and receiving paths to and from the remote system. Pairing of neighbors to form a BFD Sessions between local and remote is typically per physical port and per sub-interface, which causes large scaling problems, e.g., as number of BFD Sessions multiply and CPU computational overhead increases, and also as the number of sub-interfaces increases (e.g., >1000).